I put14500 batteries on board and plug usb in the uploader, the power light is on, and 2 lights blink for 1 second and dim, also hear some beeps. Then I test the uploader, the picture is the result I get.
Yesterday I tried Mac, and failed to upload, it displayed the port was busy. When I changed to Windows system, and upload some tests successfully( testbuzzer,testled) , but when I uploaded writeinstint, it was wrong.
Today the conditions are the same on Mac and Windows, all the uploading tests don't go through.
Similar problem, resolved by deleting/adding bluetooth connection on Mac (after almost every upload).
On my Mac it also occasionally shows uploading errors (port doesn't exist/not in sync/cannot open port, etc.). I located the problem as the disabled USB hub due to overcurrent protection. If that happens, the Tx and Rx LEDs on the uploader will keep lighting up.
I usually fix it by switching to another USB port. And if all USB ports are disabled, I restart the computer.
There's also possibility that the uploader is broken. But according to your description, it worked once and there's no much chance to burn the chip. So I suggest restarting the computer and try uploading again.
Seems the same case as an old post by Fox. But I really tried 4 different usb cables, two computers, two systems.